1. Field of the Invention
The present invention relates to wavelength selective devices. In particular, the present invention relates to dense wavelength division multiplexers (DWDMs).
2. The Prior Art
With the growing use of the Internet, users are accessing a wider variety of data, such as streaming voice and video, and as a result are placing greater demands on the existing Internet backbone. As a consequence, traditional coaxial cable, which forms the backbone of the Internet, can no longer support these increased demands. Thus, current information systems are continually being expanded to meet increasing bandwidth demands.
One viable alternative to the traditional coaxial backbone is optical fiber because of its potential for greatly increased bandwidth. Various methods have been proposed to maximize the bandwidth of optical systems.
One such system is disclosed in U.S. Pat. No. 5,809,190 (the ""190 patent) to the present inventor. Therein, a Dense Wavelength-Division Multiplexer (DWDM) is disclosed which utilizes a Fused-Biconical Taper (FBT) technique.
FIG. 1 shows a prior art diagram of a 1xc3x97N DWDM 100 according to the ""190 patent. As used herein, the symbol N indicates the number of channels that are used by a DWDM to multiplex or demultiplex a given input provided by an input fiber. The number N is equal to 2m wherein m represents the number of times a DWDM performs signal divisions for the given input signal prior to their being demultiplexed at a receiving end.
Accordingly, the prior art DWDM is known as a m-stage DWDM in which MWDM 111 is a first stage Wavelength Division Multiplexer (WDM) having a window spacing of xcex94xcex. Likewise, MWDMs 121 and 122 are a pair of second stage WDMs, each having a window spacing 2xcex94xcex. MWDMs 131, 133, and 134 are a plurality of third stage WDMs, each having a window spacing of 4xcex94xcex.
Each of the WDMs in FIG. 1 has a window with a center wavelength which varies with its sequence in the DWDM. Each stage in the DWDM 100 may be designated as 1m1, 1m2, . . . , and 1m(2mxe2x88x921), representing a m-th stage WDM of the DWDM. Regarding window spacing, the window spacing of a m-th stage MWDM is 2mxe2x88x921 xcex94xcex, which is twice as large as a window spacing demonstrated by a mxe2x88x921 stage MWDM, yet one half of the size of the window spacing of a m+1 stage MWDM. The number of stages m may be from be from 1 to n, where n=(logN/log2), forming a plurality of MWDMs, 1n1, 1n2, . . . , 1n(N/2).
Each channel of the DWDM 100 has only one window with a characteristic central wavelength corresponding to a particular center wavelength originating from the first stage WDMs. For example, in FIG. 1, each of the windows included in channel pathways 111-131 and 111-132 has a center wavelength identical to a center wavelength in corresponding window of the channel 121. Likewise, each of the windows in the channel pathways 111-133 and 111-134 has a center wavelength identical to a center wavelength in a corresponding window of the channel 122.
Referring still to FIG. 1, the operation of the DWDM 100 as a demultiplexer may now be shown. A lightwave signal having wavelengths xcex1-xcexN are provided by fiber 10 to MWDM 111. Wavelength series xcex1, xcex3, . . . , xcexNxe2x88x921 is transmitted to WDM 121, and wavelength series xcex2, xcex4, . . . , xcexN is transmitted to WDM 122. FIGS. 2A and 2B show representative spectral distributions of the wavelength series where N=8.
Referring back to FIG. 1, after demultiplexing by subsequent stages, the light signals are demultiplexed into N individual channels and distributed to N individual fibers 11, 12, . . . , 1N.
Referring now to FIGS. 3A-3E, detailed embodiments of the DWDM of the ""190 patent are shown. FIG. 3A is a logic diagram of a 1xc3x974 DWDM according to the ""190 patent, also known as a 4-channel DWDM. The first stage MWDM 311 is cascadedly connected to two second stage MWDMs 321 and 322. For demultiplexing purposes, a lightwave input having wavelengths xcex1-xcex4 are input on fiber 30, and outputs xcex1, xcex2 , xcex3 , and xcex4 are provided on fibers 31, 32, 33, and 34, respectively. For multiplexing purposes, the inputs and outputs are reversed. FIGS. 3C, 3D, and 3E show the respective insertion loss of the MWDMs 311, 321, and 322 wherein xcex94xcex is the window spacing and xcex4xcex is the window bandwidth. The dash curve and the solid curve in FIG. 3C indicates respectively the insertion loss in channels 30-321 and 30-322. The dash curve and the solid curve in FIG. 3D indicates respectively the insertion loss in channels 34-311 and 34-311. The dash curve and the solid curve in FIG. 3E indicates respectively the insertion loss in channels 33-311 and 33-311.
FIG. 3B shows an actual physical structure of the ""190 DWDM according to the ""190 patent. The first stage MWDM 311 is cascadedly connected to two second stage MWDMs 321 and 322, and the DWDM of the ""190 patent in housed in a container 35 having a length L and a width W.
As is appreciated by those of ordinary skill in the art, the length and width of container 35 is dictated by the radius R about which the optical fibers of the DWDM of FIG. 3B may be bent. As a consequence, the DWDM of the ""190 patent suffers from certain disadvantages. While satisfactory for the purposes intended in terms of performance, the DWDM of the ""190 patent suffers from size disadvantages. Due to the fused-biconical technique used in the DWMs of the ""190 patent, the minimum radius about which fibers can be bent is approximately 35 mm. Thus, the minimum finished size of a DWDM according to the""190 patent has a length L of approximately 100 mm and a width W of approximately 50 mm.
Given the need to upgrade communications system as discussed above, there is an apparent need to fabricate a DWDM which is smaller in size than DWDMs of the prior art.
The invention satisfies the above needs. The present invention relates to wavelength selective devices. In particular, the present invention relates to dense wavelength division multiplexers (DWDMs).
A miniature dense wavelength division multiplexer (DWDM) is disclosed.
In a first aspect of the present invention, a plurality of multi-window wavelength multiplexers (MWDMs) are cascaded and optically coupled to form a tree, and each of the MWDMs forming the tree comprises a microbend coupler.
In a second aspect of the present invention, the forming of the MWDM tree is characterized by the absence of the bending of optical fibers external to said microbend couplers.
A method for forming a DWDM is disclosed, which comprises providing a plurality of multi-window wavelength multiplexers (MWDMs) cascaded and optically coupled to form a tree, wherein each of the MWDMs of the tree comprises a microbend coupler.
Additional aspects of the present invention are disclosed wherein the DWDM formed by the present invention measures approximately 100 mmxc3x9750 mm, and as little as 50 mmxc3x9720 mm.